Suspended deck for liquid natural gas tank

ABSTRACT

A non-welded deck used to support insulation from the roof of a low temperature or cryogenic storage tank is disclosed. The deck may be comprised of a plurality of spaced apart bars with metal sheets covering the spaces between the bars. The edge of the metal sheets may be clamped to the bars to form the deck. The edges of adjacent metal sheets may overlap and be clamped together in such a way as to deform the sheets creating a metal-to-metal vapor and dust proof seal. The plurality of clamping bars and support bars may secure the metal sheets with sufficient strength to allow the entire deck to support loadings as a stressed membrane. The tank may be constructed with hardware that remains secure even after being subjected to repeated thermal cycling of over 200° Celsius (360° Fahrenheit).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an insulation deck suspendedfrom the roof of a low temperature tank, such as a liquid natural gastank for example.

2. Description of the Related Art

Every year more and more natural gas reserves are discovered.Unfortunately, much of it is found far from the major consumer countriesmaking economical transportation and distribution vital. Presently farmore natural gas is removed from discovered natural gas reserves than isconsumed globally. The excess amount of natural gas requires the rapidconstruction of storage facilities to hold the extracted natural gas.The size of the needed storage facilities and vessels can be decreasedif the natural gas is stored at cryogenic temperatures, which liquifiesthe natural gas. Liquifying natural gas decreases the volume of thenatural gas by more than 600 percent. Thus, liquid natural gas (“LNG”)requires less storage space than natural gas, but LNG must be stored atless than −163° Celsius (−261.4° Fahrenheit) in order to stay liquified.

Such storage vessels must be constructed of a material that is able toremain ductile and not crack at cryogenic temperatures. Generally LNGtanks are constructed of an inner tank, which must be constructed of ametal that remains ductile at cryogenic temperatures such as 9% nickelsteel, enclosed in an outer tank. The space between the inner tank andouter tank is filled with insulation of various forms to reduce the costof maintaining the LNG at cryogenic temperatures. The outer tank is notsubjected to the same cryogenic temperature and thus may be constructedof various materials such as pre-stressed concrete. These storagevessels may include an insulation deck suspended above the inner tankfrom the roof of the outer tank to aid in maintaining the inner vesselat the cryogenic temperature.

Like the inner storage vessel, the deck must be constructed of amaterial that remains ductile at −163° Celsius. Additionally, theinsulation deck must be constructed of a material so that the deck maybe able to support the loads of the insulation, insulation workmen, andinspection personnel. Various aluminum and stainless steel alloys areexcellent construction materials to be used at cryogenic materials asthey provide the necessary strength and remain ductile at coldtemperatures. Further, aluminum alloys actually increase in strength atcryogenic temperatures. However, the use of these materials in theconstruction of the deck does have some disadvantages.

One method of constructing an insulation deck of aluminum or stainlesssteel alloys is by welding the deck together and then suspending thedeck from the roof. Often the insulation deck is constructed by weldingtogether various components of the deck at ground level and oncecomplete using blowers and guide lines to float the outer roof intoposition with the deck attached. However, the time required to constructa welded deck can be lengthy as the deck must be welded together at thework site and welding can be a rather unpredictable process as aluminumis generally considered the most difficult alloy to weld. Stainlesssteel alloys are also difficult to weld in comparison to other carbonsteel alloys. Thus, the construction of such a deck requires skilledwelders, which increase the cost and time of construction. Since thedeck must be completed and attached to the outer roof prior to the airlifting of the outer roof to the top of the tank, the deck assembly isoften on the critical path of the project.

Welding together the insulation deck may also have an adverse affect onthe strength of the insulation deck. Typically, aluminum comes in heattreatable and non-heat treatable alloys. Heat treatable aluminum alloysget their strength from a process called ageing. Aluminum alloys canalso get their strength from the annealing process. However, significantdecreases in tensile strength can occur when welding aluminum due toover aging or annealing of the aluminum. In order to compensate for thedecrease in strength, often the thickness of the welded aluminum deckmust be increased thus increasing the cost and weight of the deck.Further, the increased weight of the deck increases the number and sizeof the supports suspending the insulation deck from the roof of theouter tank.

Another method of constructing a suspended insulation deck is thebolting together components consisting of corrugated metal thensuspending the corrugated metal deck from the roof. While a deckconstructed of corrugated metal bolted together may be assembledtogether more rapidly than a welded deck, this type of insulation deckpresents a limit as to the type of insulation that can be used. One typeof insulation used in LNG tanks is perlite, which is an inexpensive, buta very effective insulation material. Perlite is a very fine powder andthus, will leak through the seams of the corrugated metal deck possiblycausing contamination issues with the LNG held in the inner storagevessel. Other common insulation materials, such as fiberglass or rockwool, can also have fine particles of dust that can leak through theseams possibly causing contamination. Closing the seams with sealants orgasket materials increase the costs and such materials must be suitablefor cryogenic temperatures and repeated differential thermal cycling.

Another problem with present decks that are screwed or bolted togetheris the thermal expansion and contractions of different materials used inthe construction of the deck. Often the fasteners used in theconstruction of the insulation deck are comprised of a differentmaterial than the deck, and thus the fasteners and the deck contract andexpand differently. The difference of expansion and contraction canloosen the fasteners of the deck due to the thermal cycling of thestorage vessel. LNG tanks may be subjected to thermal cycling of atleast 200° Celsius (360° Fahrenheit), the difference between typicalsummertime ambient temperatures and the cryogenic temperature needed tosustain the LNG in liquified form. This thermal cycling may occur due toroutine maintenance of the LNG tank.

In light of the foregoing, it would be desirable to provide aninsulation deck and method of construction that does not require askilled welder to construct. It would also be desirable for a deck thatmay be constructed in a minimal amount of time. Further, it would bedesirable to provide a deck and method of construction that would havestructural integrity during thermally cycling of at least 200° Celsius.Additionally, it would be desirable to construct a deck without weldingon which a fine powdered insulation, such as perlite, or otherinsulation materials which contain dust or fine fibers could be usedwithout the chance of contaminating the stored LNG. It would also bedesirable for the deck to be constructed such that the vapors from theLNG could not escape through the seams of the deck.

The present invention is directed to overcoming, or at least reducingthe effects of, one or more of the issues set forth above.

SUMMARY OF THE INVENTION

The apparatus of one embodiment of the present disclosure is aninsulation deck that is constructed by assembling aluminum componentswithout welding and prevents the contamination of material, such as LNG,stored in a low temperature tank from the insulation supported by theinsulation deck. As used herein, a low temperature tank is a tank inwhich temperatures within the tank reach cryogenic temperatures and theterm low temperature tank may be utilized interchangeably with LNG tank,cryogenic tank, and the like, and each term (low temperature tank, LNGtank, cryogenic tank) is to be given its ordinary meaning.

The insulation deck is constructed such that metal-to-metal seals arecreated at the junction between the deck components creating aninsulation deck without any cracks or seams for insulation to leakthrough contaminating the stored material. Additionally, the deckincludes a sealing member that extends from the edges of the deck to thesides of the low temperature tank.

One embodiment of the present disclosure is an insulation deck for usein a low temperature tank comprising a plurality of beams, a pluralityof support bars connected to the plurality of beams, a plurality ofmetal sheets wherein an external portion of each of the metal sheetsrests on one of the support bars and covers openings between the supportbars, a plurality of clamping bars that engage a top surface of at leastone the metal sheets, and a plurality of fasteners that secure theclamping bars to the support bars. The plurality of clamping bars andsupport bars may secure the metal sheets with sufficient strength toallow the entire deck to support loadings as a stressed membrane.Additionally, one embodiment of the insulation deck may include atermination member extending around the edge of the insulation deck. Theplurality of fasteners may be lock bolts. Alternatively, the pluralityof fasteners may be mechanically locked in place. Insulation may beplaced on the plurality of metal sheets. In one embodiment, theinsulation may be a fine powder, such as perlite, or may containsignificant dust components.

In one embodiment of the present disclosure, the insulation deck may becomprised of a plurality of beams that are aligned substantiallyparallel, a plurality of support bars connected to the plurality ofbeams that are aligned substantially parallel and substantiallytransverse to the beams, a plurality of metal sheets wherein an externalportion of each of the metal sheets rests on one of the support bars andcovers openings between the support bars, a plurality of clamping barsthat engage a top surface of at least one the metal sheets, and aplurality of fasteners that secure the clamping bars to the supportbars. The components of the insulation deck, namely the parallel beams,the support bars, the metal sheets, the clamping bars, and the fastenersmay each be comprised of an aluminum alloy. However, the componentscould all be comprised of the same material, but not necessarily bealuminum alloy, so that the expansion and contraction rates of the deckcomponents are uniform.

In one embodiment, the insulation deck may include means for suspendingthe insulation deck from the roof of a low temperature tank. The meansfor suspending the insulation deck may include metal bars, structuralbeams, metal cables, or stainless steel cables. The means for suspendingthe insulation deck may be connected to the plurality of beams.Alternatively, the means for suspending the insulation deck may beconnected to plurality of fasteners. The insulation deck may besuspended from the roof of a low temperature tank using variousstructures, such as bars or cables, as would be appreciated by one ofordinary skill in the art having the benefit of this disclosure.

The metal sheets of the insulation deck may be substantiallyrectangular, but the size and shape of the sheets may be varied as wouldbe appreciated by one of ordinary skill in the art having the benefit ofthis disclosure. The metal sheets may be at least partially deformed bythe clamping bars when the clamping bars are secured to the support barsby the fasteners. Adjacent metal sheets may overlap at the edges and assuch the deformation of the sheets caused by the clamping bars maycreate a metal-to-metal seal between the sheets. Likewise, thedeformation of each sheet may create a metal-to-metal seal between thesheet and the clamping bar and/or between the sheet and the support bar.

In one embodiment at least one of the support bars may include a rib andat least one of the clamping bars may include a groove that mates withthe rib. The rib on the support bar may deform a portion of the metalsheet into the groove when a fastener is tightened. Alternatively thesupport bar may include a groove while the clamping bar includes amating rib and again a portion of a metal sheet may be deform into thegroove by the mating rib when a fastener is tightened. In an alternativeembodiment, at least one of the support bars may include a channelrunning along the support bar and at least one of the clamping bars maypartially deform one of the metal sheets into the channel.

In one embodiment the plurality of support beams and plurality ofclamping beams have interfitting convex and concave surfaces. Twoadjacent metal sheets of the plurality of metal sheets may overlap suchthat a portion of the metal sheets rest between the convex and concavesurfaces. The overlapping portion of the metal sheets may at least bepartially deformed by the support beam and clamping beam when a fasteneris tightened. The deformation of the overlapping portion may create ametal-to-metal seal.

One embodiment of the present disclosure is the method of constructingan insulation deck for use in a low temperature tank that comprises thesteps of attaching a plurality of substantially parallel beams to theroof of the low temperature tank; attaching a plurality of substantiallyparallel support bars to the beams wherein the support bars extendtransversely across the beams; placing a plurality of metal sheetsacross the openings between the support bars; placing a plurality ofclamping bars on the metal sheets locating the clamping bars above thesupport bars; deforming at least a portion of the metal sheets bytightening a plurality of fasteners, wherein the fasteners securetogether the support bars, metal sheets, and clamping bars; attaching asealing member that extends from the edge of the insulation deck to thesides of the low temperature tank; and installing insulation on top ofthe insulation deck.

The method may further include the step of overlapping the edges of themetal sheets. Additionally, the portion of the metal sheets that isdeformed may be the overlapping edges. The insulation used in the methodof constructing the insulation deck may be a fine powder or contain asignificant amount of dust. In one embodiment of the method ofconstructing the insulation deck the parallel beams, the support bars,the metal sheets, the clamping bars, and the fasteners are all comprisedof an aluminum alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of one embodiment of an insulation deck 1 for alow temperature tank 2 of the present disclosure comprised of a networkof metal sheets 10 clamped together.

FIG. 2 shows a cross-section of the present embodiment of two metalsheets 10 that overlap between a support bar 20 and a clamping bar 30.

FIG. 3 shows the embodiment of FIG. 2 with a lock bolt 40 insertedthrough opening 5 of the clamping bar 30 and opening 15 of the supportbar 20.

FIG. 4 shows the embodiment of FIG. 3 with the collar 50 swaged onto thelock bolt 40 and the pigtail 60 broken off of the lock bolt 40.

FIG. 5 shows one embodiment of a perimeter plate 100 that closes the gapbetween an insulation deck and an inner tank of a low temperature tank.

While the invention is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the invention is not intended to be limitedto the particular forms disclosed. Rather, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments of the invention are described below as theymight be employed in the use of the design for an insulation decksuspended from the roof of a LNG vessel or other fluid storage tank. Inthe interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

Further aspects and advantages of the various embodiments of theinvention will become apparent from consideration of the followingdescription and drawings.

As shown in FIG. 1, an insulation deck 1 for a low temperature tank 2 ofthe present disclosure may be comprised of a network of metal sheets 10clamped together. As shown in FIGS. 2-4, the insulation deck 1 may beconstructed by clamping a metal sheet 10 between a support bar 20 and aclamping bar 30. The assembly of the metal sheet 10, the support bar 20,and the clamping bar 30 may be secured together by a fastener 40. Thesupport bar 20 may be connected to a beam 90 that is substantiallyperpendicular to the support bar 20. The insulation deck 1 may besuspended from the roof of the low temperature tank 2 by cables or barsconnected to the beam 90.

As shown in FIG. 2, an embodiment of the present disclosure may becomprised of adjacent metal sheets that overlap between a support bar 20and a clamping bar 30. The support bar 20 may contain a central opening15 through its top surface 25. The top surface 25 of the support bar 20may be concave in shape as shown in FIG. 2. The clamping bar 30 maycontain a central opening 5 through its bottom surface 35, which may beconvex as shown in FIG. 2. Alternatively, the top surface of the supportbar 20 and the bottom surface of the clamping bar may be flat and mayadditionally include a groove along its surface as would be appreciatedby one of ordinary skill in the art having the benefit of thisdisclosure.

The support bar 20 includes a flange 26 on the end opposite of the topsurface 25. As would be appreciated by one of ordinary skill in the arthaving the benefit of this disclosure, the shape of the flange 26 couldbe varied and the flange 26 could be used to connect a beam 70 to thesupport bar 20. For example, a fastener could be inserted through theflange 26 into the beam 70 to fasten the support bar 20 to the beam 70.Likewise, clamping bar 30 may include a flange 36, of which the shapecould be varied. The flange 36 of the clamping bar could be used to thesecure the clamping bar 30 to a beam 70 or other structure.

As shown in FIG. 3, a fastener 40 may be inserted through opening 15 inthe support bar 20 and opening 5 in the clamping bar 30. The fastener 40may be a lock bolt that includes a collar 50 and a pig tail 60, as shownin FIG. 3, but could be any applicable fastener as would be recognizedby one of ordinary skill in the art having the benefit of thisdisclosure. The metal sheets 10 could be provided with pre-fabricatedopenings (not shown) to aid in the assembly of the deck or alternativelyopenings could be created in the metal sheets during the constructionprocess. A tool 60 is used to swedge the collar 50 onto the serratedportion of the fastener 40. The tool 60 applies downward force orpressure to the collar 50 causing the collar to deform onto the fastener40 locking it in place. The tool 60 may apply the necessary pressurethough hydraulics, pneumatics, or other means as would be apparent toone of ordinary skill in the art having the benefit of this disclosure.

The force applied by the tool 60 to swedge the collar 50 may break offthe pigtail 70 of the fastener 40, as shown by FIG. 4. By swedging thecollar 40 onto the fastener 40, the shank of the fastener 40 is put intotension. The tension of the fastener 40 and the collar 40 locks thesupport bar 20 and clamping bar 30 together and prevents the assemblyfrom loosening due to thermal cycling of the tank in which it may beinstalled. Additionally, the swedging of the fastener 40 pulls thesupport bar and clamping bar 30 together causing the deformation of theoverlapping metal sheets 10 clamping between the bars. The deformationof the metal sheets creates a metal-to-metal seal between the sheets.The convex surface of the clamping bar and the concave surface of thesupport bar cause the metal sheets to deform with substantially the samecurvature as the surfaces. The mating convex and concave surfaces aid informing a metal-to-metal seal between the overlapping metal sheets 10.The configuration and geometries of the surfaces of the both the supportbar and clamping bar can be varied, such as including a groove in thesurface, as would be apparent to one of ordinary skill in the art havingthe benefit of this disclosure.

The insulation deck 1 may be located above an inner tank of the lowtemperature tank 2 such that there is a gap between in the insulationdeck and the inner tank. A perimeter plate 100, as shown in FIG. 5, maybe used to connect the gap between the insulation deck 1 and the innertank. The perimeter plate 100 may be comprised of polygonal beams 105connected together with brackets 110. The polygonal beams 105, brackets110, and fasteners 115 connecting the beams and brackets may all becomprised of the same material, such as an aluminum alloy for example,to allow for a uniform expansion and contraction rate as the perimeterplate may be subjected to thermal cycling. The perimeter plate can beconstructed using a number of different designs and components as wouldbe apparent to one of ordinary skill in the art having the benefit ofthis disclosure.

Although various embodiments have been shown and described, theinvention is not so limited and will be understood to include all suchmodifications and variations as would be apparent to one skilled in theart.

1. A insulation deck for use in a low temperature tank, comprising: aplurality of beams; a plurality of support bars connected to theplurality of beams; a plurality of metal sheets, wherein an externalportion of each of the plurality of metal sheets rests on one of theplurality of support bars and the plurality of metal sheets coveropenings between the plurality of support bars; a plurality of clampingbars, wherein each of the plurality of clamping bars engages a topsurface of at least one of the plurality of metal sheets; and aplurality of fasteners, wherein at least one of the plurality offasteners secures at least one of the plurality of clamping bars to atleast one of the plurality of support bars.
 2. The insulation deck ofclaim 1, further comprising a termination member extending around theedge of the insulation deck.
 3. The insulation deck of claim 1, whereinthe plurality of fasteners are lock bolts.
 4. The insulation deck ofclaim 1, wherein the plurality of fasteners are mechanically locked inplace.
 5. The insulation deck of claim 1, wherein the plurality of beamsare aligned substantially parallel and wherein the plurality of supportbars are aligned substantially parallel and substantially transverse tothe plurality of beams.
 6. The insulation deck of claim 5, wherein theplurality of substantially parallel beams, the plurality ofsubstantially parallel support bars, the plurality of metal sheets, theplurality of clamping bars, and the plurality of fasteners are eachcomprised of an aluminum alloy.
 7. The insulation deck of claim 6,further comprising means for suspending the insulation deck from theroof of the low temperature tank.
 8. The insulation of deck of claim 7,wherein the means for suspending the insulation deck is connected to theplurality of beams.
 9. The insulation deck of claim 7, wherein theplurality of fasteners connect the means for suspending the insulationdeck to the plurality of support bars or to the plurality of clampingbars
 10. The insulation deck of claim 7, wherein the means forsuspending the insulation deck is metal bars or structural beams. 11.The insulation deck of claim 7, wherein the means for suspending theinsulation deck is metal cables.
 12. The insulation deck of claim 11,wherein the metal cables further comprise stainless steel cables. 13.The insulation deck of claim 6, wherein the insulation deck is suspendedfrom the roof of the low temperature tank from the group consisting ofmetal bars, structural beams, or metal cables.
 14. The insulation deckof claim 1, wherein at least one of the plurality of support bars has atleast one rib and at least one of the plurality of clamping bars has atleast one groove that mates with the at least one rib such that at leasta portion of one of the plurality of metal sheets is pressed into thegroove by the rib when at least one of the plurality of fasteners istightened.
 15. The insulation deck of claim 1, wherein at least one ofthe plurality of support bars has at least one groove and at least oneof the plurality of clamping bars has at least one rib that mates withthe at least one groove such that at least a portion of one of theplurality of metal sheets is pressed into the groove by the rib when atleast one of the plurality of fasteners is tightened.
 16. The insulationdeck of claim 1, wherein the plurality of support beams and theplurality of clamping beams have interfitting convex and concavesurfaces.
 17. The insulation deck of claim 16, wherein at least twoadjacent metal sheets of the plurality of metal sheets overlap such thata portion of the metal sheet rests between the concave and convexsurfaces.
 18. The insulation deck of claim 17, wherein at least one ofthe plurality of clamping bars and at least one of the plurality ofsupport beams partially deforms a portion of the metal sheets when atleast one of the plurality of fasteners is tightened.
 19. The insulationdeck of claim 18, wherein the deformation of the portion of the metalsheets creates a metal-to-metal seal.
 20. The insulation deck of claim1, wherein the plurality of beams, the plurality of support bars, theplurality of metal sheets, the plurality of clamping bars, and theplurality of fasteners are each comprised of the same material.
 21. Theinsulation deck of claim 1, wherein at least one of the plurality ofsupport bars further comprises a channel running along the support bar.22. The insulation deck of claim 21, wherein at least one of theplurality of clamping bars at least partially deforms a portion of oneof the plurality metal sheets into the channel running along the supportbar.
 23. The insulation deck of claim 1, wherein the plurality offasteners are tightened such that the plurality of clamping bars and theplurality of support bars causes the plurality of metal sheets to be astressed membrane.
 24. The insulation deck of claim 23, furthercomprising insulation supported by the stressed membrane.
 25. Theinsulation deck of claim 24, wherein the insulation is a powder.
 26. Theinsulation deck of claim 1, further comprising insulation supported onthe plurality of metal sheets.
 27. The insulation deck of claim 26,wherein the insulation is a powder.
 28. The insulation deck of claim 27,wherein the insulation is perlite.
 29. The method of constructing aninsulation deck for use in a low temperature tank, comprising: attachinga plurality of substantially parallel beams to the roof of the lowtemperature tank; attaching a plurality of substantially parallelsupport bars to the plurality of substantially parallel beams, whereinthe plurality of support bars extend transverse to the plurality ofbeams; placing a plurality of metal sheets across the openings betweenthe plurality of support bars; placing a plurality of clamping bars onthe plurality of metal sheets, wherein the plurality of clamping barsare located above the plurality of support bars; deforming at least aportion of the plurality of metal sheets by tightening a plurality offasteners, wherein the plurality of fasteners secure together theplurality of support bars, the plurality of metal sheets, and theplurality of clamping bars; attaching a sealing member that extends fromthe edge of the insulation deck to the sides of the low temperaturetank; and installing insulation on top of the insulation deck.
 30. Themethod of claim 29, wherein each of the plurality of substantiallyparallel beams, the plurality of substantially parallel support bars,the plurality metal sheets, the plurality of clamping bars, and theplurality of fasteners are comprised of aluminum.
 31. The method ofclaim 29, wherein the insulation is a powder.
 32. The method of claim31, wherein the insulation is perlite.
 33. The method of claim 29,wherein the plurality of metal sheets are a stressed membrane.
 34. Themethod of claim 29, further comprising the step of overlapping the edgesof the plurality of metal sheets.
 35. The method of claim 34, whereinthe at least a portion of the plurality of metal sheets that is deformedis the overlapping edges of the plurality of metal sheets.